The invention relates to a method for continuously producing 2-butanone from 2,3-butanediol in hot pressurized water having an added electrolyte.
2-Butanone is primarily used as a fuel additive and as a solvent for varnishes, plastics, resins, nitrocellulose and acetyl cellulose. In addition, it is also used for deparaffinization of lubricating oils. A considerably lower proportion of 2-butanone is used as a starting material for preparing methyl isopropenyl ketone and methyl and ethyl amyl ketone. In the presence of hydrogen peroxide, methyl ethyl ketone is converted to methyl ethyl ketone peroxide, a polymerization initiator.
The reaction of polyols having hydroxyl groups in the 1,4-positions, such as 1,4-butanediol, gives rise to the corresponding tetrahydrofuran derivatives. In contrast, the dehydration of diols having neighbouring hydroxyl groups, for example 1,2-propanediol and 1,2-butanediol, yields the corresponding aldehyde or ketone.
The dehydration of 2,3-butanediol has previously been carried out by means of heterogeneous and homogeneous catalysis. Aluminosilicates (A. N. Bourns, R. V. V. Nicholls, Can. J. Res. B 1946-1947, 24-25, 80 ff) and Nafion®-H (I. Bucsi, A. Molnár, M. Bartók, Tetrahedron 1994, 50, 27, 8195 ff) were used as heterogeneous catalysts. Sulfuric acid (A. C. Neish, V. C. Haskell, F. J. MacDonald, Can. J. Res. B 1945, 23, 281 ff) or phosphoric acid (E. R. Alexander, D. C. Dittmer, J. Am. Chem. Soc. 1951, 73, 1665 ff) were used for homogeneously catalysed dehydration. In all experiments, 2-butanone and isobutyraldehyde, and also its acetal with 2,3-butanediol, were obtained in varying proportions. Bourns was able to obtain 2-butanone in 85% yield in a gas phase reaction at 225° C. over aluminosilicate. The yield declined at higher temperatures, while above 450° C. only gaseous decomposition products were formed. Bucsi likewise achieved a selectivity for 2-butanone of 83% with almost complete conversion, by heterogeneous catalysis over Nafion®-H catalysts, while the formation of isobutyraldehyde could be almost completely eliminated (S=3%). Neish investigated the kinetics of dehydration to 2-butanone with addition of 3-20% (g g−1) sulfuric acid. For the rac-meso starting materials (isomeric mixture of (R,R)- and (S,S)- and meso-2,3-butanediol), distillation with 85% phosphoric acid results in a combined yield of 2-butanone and isobutyraldehyde of 59%. The use of high acid concentrations, however, is accompanied by increased corrosion of the reactor. Furthermore, an additional neutralization is required during workup.
It is also known that, by addition of zinc sulfate and nickel sulfate in subcritical and supercritical water, the conversion of polyols and also the yield can be increased. On dehydration of meso-erythritol to the major product 1,4-anhydroerythritol in water, the maximum yield is 55% at 360° C., 340 bar and with 988 ppm (g g−1) zinc sulfate. Starting from 1,2-propanediol in sub- and supercritical water, the maximum yield of propionaldehyde achieved is 90% at 360° C., 340 bar, residence time 120 s and with 400 ppm (g g−1) zinc sulfate. At 320° C., 34 MPa and a residence time of 90 s, the conversion is approx. 70% and the yield is 70% (L. Ott, S. Kohl, M. Bicker, H. Vogel, Chem. Eng. Technol. 2005, 28, 1561). On conversion of 1,2-butanediol to n-butyraldehyde in the presence of 400 ppm (g g−1) zinc sulfate at 340° C. and 340 bar, a maximum yield of 70% is achieved after a residence time of 120 s (L. Ott, V. Lehr, S. Urfels, M. Bicker, H. Vogel, J. Supercrit. Fluids 2006, 38, 80 ff). This reaction procedure is unfavourable since zinc sulfate is very expensive and nickel sulfate is classified as environmentally harmful according to the hazardous substance regulations.
The object of the invention is to provide a method which optimizes the continuous production of 2-butanone from 2,3-butanediol in hot pressurized water having an added electrolyte.